Ester lubricants



United States Patent US. Cl. 252-466 5 Claims ABSTRACT OF THE DISCLOSURE l ubricating oil compositions having excellent anticorrosion and antioxidant properties consist of a major amount of an ester base lubricating oil and minor amounts each of a triaryl phosphorothionate and triaryl phosphate.

The present invention relates to ester lubricants. More particularly this invention relates to ester lubricants containing a mixture of phosphorus ester additives. Lubricants which are suitable for the lubrication of aviation gas turbines should possess a good oxidation stability at high temperatures and good extreme pressure properties. Such lubricants normally contain antioxidants, such as certain substituted phenothiazines and certain secondary aromatic amines and certain extreme pressure additives, such as triaryl esters of phosphorothionic acid.

Although these triaryl phosphorothionates have useful extreme pressure properties in ester lubricants, they cause corrosion of certain metals, in particular magnesium, cadmium and 8.82 steel. This steel is an aircraft gear quality steel meeting British Standards Specification EN 39B.

Triaryl phosphates are well known extreme pressure additives, but ester lubricants containing them are de ficient in high temperature oxidation stability.

It has now been found that triaryl phosphorothionates and triaryl phosphates work together in ester lubricants With respect to anticorrosion properties and antioxidant properties at high temperatures.

According to the present invention an ester lubricant comprises a major proportion of an ester lubricating oil and minor proportions each of a triaryl phosphorothionate and a triaryl phosphate.

The triaryl phosphorothionates useful in this invention contain 6 to 10 carbon atoms in each aryl group. The aryl groups in each triaryl phosphorothionate may be the same or different. Examples of suitable triaryl phosphorothionates include triphenyl-, tritolyl-, tribenzy1-, trixylyland diphenyltolyl-phosphorothionate. The preferred phosphorothionate is triphenyl phosphorothionate (TPPT).

The triaryl phosphates useful in this invention also contain 6 to 10 carbon atoms in each aryl group which may be the same or different. Suitable phosphates include triphenyl-, tritolyl-, tribenzyl-, trixylyland diphenyltolylphosphate. The preferred phosphate is triphenyl phosphate (TPP).

The ratio of triaryl phosphate to triaryl phosphorothionate in the lubricant may vary from 0.25:1 to 1:1, preferably the ratio will not be less than 05:1. The combined triaryl phosphates and triaryl phosphorothionates are present in an amount sufficient to provide anticorrosion and antioxidant properties. In general they will be present in an amount of 0.05 to 10% by weight and preferably from 0.1 to 5% by weight of the final composition.

Esters suitable as base oils in the present lubricant are simple esters, complex esters, polyesters, or mixtures 3,483,122 Patented Dec. 9, 1969 thereof. Thickeners may be added depending upon the viscometric properties desired for the composition and the temperature conditions under which it is to be used. By simple ester is meant an ester formed between an aliphatic dicarboxylic acid and aliphatic monohydric alcohol, preferred simple esters being formed from an aliphatic dicarboxylic acid containing from 6 to 10 carbon atoms in the molecule and a branched chain monohydric alcohol containing from 6 to 12 carbon atoms in the molecule, especially those alcohols having no hydrogen on the beta carbon atom. Examples of simple esters useful for the purposes of the present invention are diisononyl sebacate, di(Z-ethylhexyl) sebacate, diisooctyl azelate, diisodecyl azelate, di(3,5,5-trimethyl hexyl) adipate, 2- ethyl hexyl-3,5,5-trimethyl hexyl sebacate and such simple hindered esters as 2,2,4-trimethyl pentyl azelate.

By complex ester is meant an ester formed from various combinations of an aliphatic dicarboxylic acid, a glycol or polyglycol and either or both of an aliphatic monohydric alcohol and an aliphatic monocarboxylic acid. Some typical complex ester structures are represented by AD(GD)nA, A(DG)nM and MG(DG)nM, wherein A, D, G and M represent the esterification residues from an aliphatic monohydric alcohol, an aliphatic dicarboxylic acid, a glycol or polyglycol and an aliphatic monocarboxylic acid respectively and n is a number from 1 to 6. Examples of typical starting materials suitable for the preparation of such esters are Z-ethyl butyl alcohol, 2- ethyl hexyl alcohol, caproic acids, pelargonic acid, capric acid, tertiary acids (none-hydrogen acids), neopentyl glycol, ethylene glycol, propylene glycol, polyglycols such as polyethylene glycols, sebacic acid, adipic acid, azelaic acid and pimelic acid.

By polyesters is meant esters made from aliphatic alcohols having therein at least 3 hydroxyl groups, for example esters made from trimethylol propane, e.g. trimethylol propane tripelargonate. Tetra esters such as the pentaerythritol tetra-esters or the dimers or trimers of the same and dipentaerythritol esters of C C fatty acids, especially C C fatty acids are preferred. These esters are commercially available from Hercules Chemical Company.

Thickeners may also be added to the oils of the invention to improve viscosity properties. As thickeners there may be used polymers of esters of acrylic or an alkylsubstituted acrylic acid, for example, lauryl methacrylate, or an ether of a polyoxyalkylene glycol of the general formula R50(R7O) R wherein R is an alkyl group, R is hydrogen or an alkyl group, R is an alkylene group of 2 to 4 carbon atoms and n is a number greater than unity. Suitable compounds are marketed under the trade name Ucon, specific examples being LB385, LB525, LB625. Also suitable are copolymers of propylene oxide and ethylene oxide marketed under the trade name Oxilube, e.g. Oxilube /140. The thickeners may be used in proportions of up to 50% by Weight calculated on the final lubricant composition depending upon the viscometric properties required for said lubricant.

The ester lubricants of the present invention may also contain extreme pressure additives, antioxidants, metal deactivators anticorrosion agents, antifoaming agents, dye stuffs and other additives know to be useful in ester base lubricant formulations.

Suitable additional extreme pressure additives which may be used in the invention are the clorinated dior polyphenyls, i.e. diphenyls, terphenyls, higher polyphenyls or mixtures thereof containing at least one chlorine atom attached directly to each benzene nucleus, for example chlorinated dior polyphenyls sold under the trade name Arochlor. Particularly useful as E.P. additives are the monochloromethyl phosphonic acid salts of tertiary alkyl primary amines, for example the monochloromethyl phosphonic acid salts of C1842 tertiary alkyl primary amines.

Suitable as antioxidants are the substituted phenothiazines, secondary aromatic amines, alkylated phenols To illustrate the effectiveness of the compositions of the present invention the compositions shown in Table l were prepared. Compositions AE are not in accordance with the present invention and are included for comparative purposes. Compositions F] were formulated and bisphenols. 5 according to the invention.

TABLE 1 Composition, Percent Weight A B C D E F G H .l

Hercolube A e 64. 5 64. 5 64. 5 64. 5 64. 5 64. 5 64. 5 64. 5 64. 5 Hcrcolubo F 31. 9 31. 9 31. 9 31. 31. 9 31. 9 31. 9 31. 9 31. 9 N-benzyl-S.T-dioctylphenothiazine- 1. 7 1. 7 1. 7 1. 7 1. 7 1. 7 1. 7 1. 7 1. 7 Phenyl-alphanaphthylamine 1. 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 Azelaic acid 0. O2 0. 02 0. 02 0. O2 0. 02 O 02 0. O2 0. 02 0. 02 Silicone fluid MS 200/12500 n 5 5 5 5 5 5 u 5 5 5 JMT/MCMPA d 0. 17 0.17 0.17 0.17 0 17 0.17 0. 17 0.17 0. 17 3-amino4'yphenyl-l,2,4triazole 0. 2 0. 2 0. 2 0. 2 0.2 0.2 0. 2 0. 2 0. 2 Triphenylphosphorothionate 0. 5 .0 1. 0 1. 0 0. 5 1. 0 Tnphenylphosphate 0. 5 1. 0 0. 5 1.0 0. 5 0. 3

Pentaerythritol esters of saturated fatty acids.

b Dipentaerythritol esters of saturated fatty acids.

e Parts per million.

d Gill-Z2 tertiary alkyl primary amine salts of monochloromethyl phosphonic acid.

Particularly suitable as an anti-oxidant is a substituted phenothiazine having the formula:

where R is an alkyl, aryl, alkaryl, aralkyl or cyanoalkyl The following tests were carried out on the ab ve compositions and the results are given below in Tables 2-6.

Bristol siddeley corrosion test TABLE 2 Weight Change, mg./sq. cm.

Alumin- {s 8.82 Cast 8110B e Cad- Magne- Composition Brass Monel lum Bronze Steel Iron Silver Steel mium sium Nickel 2. 0 Nil Nil 0. 14 19 2. 7 Nil 0. 24 11 130 Nil 0. 56 Nil +0. 04 Nil -0. 19 -0. 64 -0. 06 +0. 07 --2. 7 --28 +0. 04 0. 74 Nil Nil Nil 0. 17 0. 46 +0. 04 Nil 0. 69 29. 8 -0. 06 0. 70 +0. 10 0. 03 0. 2 21.0 -4. 03 +0.01 1. 59 49. 0 130 +0.03 -0. 13 Nil Nil -0. 07 -0. 37 Nil Nil Nil 3. 9 12 +0. 08 +0. ()1 Nil Nil Nil Nil Nil Nil Nil 2. 9D -11. 1 +0. 07

Nil Nil Nil Nil Nil Nil Nil Nil 3. 20 l0. 4 Nil 0. 51 Nil Nil 0. 13 5. 1 0. 81 N11 0. O4 0. 51 -100 +0. 1 0

B S110B Steel is a corrosion resistant welding quality stainless steel meeting British Standards Spec. En58C.

radical and at least one of R R R and R is an alkyl or alkoxy radical, any other being hydrogen and a secondary aromatic amine having two aromatic groups directly attached to the nitrogen atom. Especially useful are the combination l0-benZyl-3,7-dioctyl phenothiazine and phenyl-alpha-naphthylamine as taught in US. Patent 3,344,068.

A wide variety of material may be used as metal deactivators and anticorrosion agents, depending on the metal or metals with which the ester base composition of the present invention will come into contact. Materials which are particularly useful as affording protection of, for example, copper, copper alloys and silver against c rrosive attack are the triazoles, for example 1,2,3-benztriazole, methyl 1,2,3 benztriazole, 3-amino-5-methyl- 1,2,4-triazole, especially 3-arnino 5-phenyl-1,2,4-

triazole, 3-amino-5-pyridyl 1,2,4- triazole, 3-amino S-anilido 1,2,4-triazole and 5,5-diamino 3,3-bi (1,2,4,-triazole) used in amounts up to about 1%, preferably about 0.5% by weight of the This test comprises bubbling air saturated with water vapor, at a fixed rate, through 50 ml. of the ester composition to be tested for a period of 24 hours at 250 C. Deterioration of the composition due to oxidation is then measured in time of viscosity change as shown in Table 3. The results shown are for duplicate runs.

TABLE 3 Percent Increase in Viscosity at F.

Composition:

From Table 3 it is clear that there is a high temperature co-antioxidant effect between triphenyl phosphorothionate and triphenyl phosphate,

Rolls-Royce corrosion test method 1002 The above corrosion test determines weight changes of selected metals suspended in test compositions at a temperature of 200 C. for 192 hours.

Prior to the test the test compositions are pretreated by heating about 100 mls. of the composition in a stainless steel container with a close fitting cap fitted with a narrow steel condenser for 5 hours at 325 C.

The results of the above test are given in Table 4.

TABLE 4 Metal Weight Change, mgJsq. cm.

Ni/Cr High Case High Cu/Ni/ Mild Pb C/Cr Pb Hardened Speed Composition A1 Ti/Cu Si Steel Bronze Steel Brass Steel Steel Cu D Nil Nil--- -1.2 s.9 -1.2 -3.7 -2.1 -0.27 -0.03 -1.5 E Nil Nil 1.8 36 -4.3 -16 --6.4 -21 -6.3 -2.0 G Nil .Ni1 0.94 6.1 0.86 2.9 1.8 -2.6 0.23 1.5

The results of Table 4 indicate that the corrosivity re- TABLE 6 snlting from the use of triphenyl phosphorothionate at high temperatures is greatly diminished when triphenyl Composmon phosphate is added to the composition. Eslter Ester plus A danger of using triphenyl phosphate in an ester Saute 1% gf i r i lubricant is that a phosphate can be hydrolysed to an acid 25 L d ht 1 2 o F f phosphate which can then catalyze the partial hydrolytic gg ggg g gg g i 5 a f (119 degradation of the ester to its half ester which is corrosive. Moreover the alcohol which is formed lowers the flashpoint. The hydrolytic tendency of the composition of this invention has been examined by means of two well-known and accepted tests, namely, the Rolls-Royce Hydrolytic Stability Test and the S.O.D. Lead Corrosion/Storage Stability Test.

The Rolls-Royce Hydrolytic Stability Test involves heating 250 mls. of a composition with 25 mls. distilled water at 90 C. until the acidity value increases by 1.5 mgms. KOH/gm. In the S.O.D. Test a lead test piece and a copper catalyst piece are mounted on a stirrer immersed in the composition under test and rotated at a specific speed. Air is bubbled through the composition, maintained at 325 F., at a specified flow rate for 1 hour. The above is carried out on a new composition and after the composition has been stored for 7 days at 230 F.

Table 5 gives the results of these two tests.

The above results indicate that the triphenyl phosphate We claim as our invention:

1. A lubricating composition containing a major amount of a carboxylic ester base lubricating oil and a minor amount, sufficient to inhibit corrosion and provide high temperature stability to the oil, each of a triaryl phosphorothionate and a triaryl phosphate in which each aryl group of the phosphorothionate and of the phosphate compounds contains 6-10 carbon atoms.

2. The composition of claim 1 wherein the triaryl phosphorothionate and triaryl phosphate comprise about 0.05 to 10% by weight of the lubricating composition.

3. The composition of claim 2 wherein the ratio of triaryl phosphate to triaryl phosphorothionate varies from 0.25:1 to 1:1.

4. The composition of claim 3 wherein the triaryl phosphorothionate is triphenyl phosphorothionate and the triaryl phosphate is triphenyl phosphate.

5. The composition of claim 4 wherein the ester base lubricating oil is a mixture of saturated fatty acid esters of pentaerythritol.

References Cited UNITED STATES PATENTS 2,080,299 5/1937 Benning et al 25246.6 3,429,813 2/ 1969 Waight et al 25246.6

FOREIGN PATENTS 663,382 5/ 1963 Canada.

DANIEL E. WYMAN, Primary Examiner J. M. HICKEY, Assistant Examiner US. Cl. X.R. 25249.8 

